This invention relates to a downhole liquid pump for use in hydrocarbon production formations and the like. Specifically, the present invention relates to a subsurface, fluid-powered, reciprocating, liquid lifting pump. The fluid powering the return stroke of the pump in the present invention is the liquid being produced or drawn from the subsurface well casing.
Presently, conventional rod actuated pumps are most commonly used in gas and oil wells to lift or withdraw liquid or condensate from the well bore. An obvious disadvantage to this type of rod pump is that the motive force to raise and lower the plunger downhole is a rigid actuator rod, and it will not compensate for bends or sharp angles in the well bore. A generally straight, vertical action of the rod must be maintained.
When hydraulic actuated reciprocating pumps are used, power fluid is usually required to be supplied to both the power and retract sides of the piston stroke. Some free-type hydraulic pumps are actuated by a flow of power fluid from the surface (either produced oil or water) down the tubing to power the pump engine. However, exhaust power fluid mixed with produced fluid returns upward through the casing annulus, or a secondary tubing string, and is separated at the surface.
The present invention utilizes a uniquely designed low volume, hydraulic pump connected to the end of a small diameter coiled tubing run. The diameter of the coiled tubing is generally in range of 1/2" to 11/8" outside diameter (OD) with the most typical size being 3/4" OD.
Because the pump of the present invention is connected to the coiled tubing, it is easily run into the standard 23/8" production well tubing, even if the well tubing has been run at an angle considerably off the true, straight, direct vertical. Further, because of the low volume of power fluid retained in the small diameter coiled tubing extending above the submerged pump, the downhole hydrostatic pressure of the produced liquid is sufficient when working against the piston head in the downhole pump to retract the pump actuator. Thus, external power only needs to be applied in the pump stroke.